Tin-plated steel sheets, electrolytic-chromate-treated steel sheets, which are referred to as tin-free steel sheets, and the like are used for various metal cans such as beverage cans, food cans, pail cans, and 18-liter cans. In particular, tin-free steel sheets are manufactured by electrolytic treatment of steel sheets in a plating bath containing hexavalent Cr and have the advantage of having excellent wet resin adhesion to resins such as paints.
In recent years, the regulations on the use of hexavalent Cr have been increasingly imposed worldwide in response to growing environmental awareness. Alternate materials to tin-free steel sheets which are manufactured using a plating bath containing hexavalent Cr have been anticipated.
Various metal cans have been manufactured conventionally by painting tin-free steel sheets or the like and forming the painted steel sheets into can bodies. In recent years, a method in which laminated steel sheets coated with resin films such as plastic films instead of paints are formed into can bodies has been widely used for the reduction of waste produced in the manufacture of cans. In such laminated steel sheets, resins need to strongly adhere to the steel sheets. In particular, since beverage or food cans are subjected to retort sterilization steps in some cases after the contents thereof are packed, laminated steel sheets used for the beverage or food cans need to have excellent wet resin adhesion such that no resin is peeled even in high-temperature, humid environments and excellent corrosion resistance such that the cans are prevented from being perforated by corrosion due to the contents of the cans even if the resin is partially detached by scratching or the like.
In response to these needs, the inventors of the present invention have shown in patent document 1 that it is possible to manufacture a surface-treated steel sheet, which has excellent wet resin adhesion and excellent corrosion resistance, without using Cr by forming a corrosion-resistant film that includes at least one layer selected from a Ni layer, a Sn layer, an Fe—Ni alloy layer, an Fe—Sn alloy layer, and an Fe—Ni—Sn alloy layer on at least one surface of a steel sheet; and then forming an adhesive film by performing a cathode electrolytic treatment in an aqueous solution containing ions containing Ti and ions containing at least one metal selected from Co, Fe, Ni, V, Cu, Mn, and Zn.
Patent Document
    Patent document 1: Japanese Unexamined Patent Application Publication No. 2009-155665